Interview Question: Cross Multiply

cross_multiply.rb

def cross_multiply(a, b)
  shorter, longer = a.size < b.size ? [a, b] : [b, a]
  shorter.cycle.take(longer.size).zip(longer).map { |n| n.reduce(:*) }
end

# Given two arrays with different, non-zero lengths, multiply each item at their same index between arrays.
# After reaching the end of the shorter array but before the end of the longer array, 
# start back at the beginning of the shorter array.

# Example
#
# (algebraically)
# cross_multiply [a, b, c, d, e], [f, g]
# #=> [af, bg, cf, dg, ef]
#
# (real values)
# cross_multiply [1, 2, 3], [4, 5, 6, 7]
# #=> [4, 10, 18, 7]